Method of constructing a porous wall



Oct. 28, 1958 2,857,657

H. L. WHEELER, JR

METHOD ,OF CONSTRUCTING A POROUS WALL Filed Jan. 16,' 1956 BY ou Mw Arrow/var:

Patented O'ct: 28; .1.958

ynited Sitatcs PatentV @ffice IVIII'BTHD' 0F' 'CONSTRUCTING- A. PGROUS WALL ,Lawrie-clean., La Canada', Calif., assignor ,to

alif "rnitr 'Institute' Research VFoundation, Pasadena, Ca'lihya corporation-of California Application January 16, ,1956, Serial N 0.559,153.

`8 Claims. (Cl. 29d-156.8)-

My, nventionrelates to constructing a .porous wall, and

.is.a continuation-impart of -my previousy application Serial N=33'5,670 -filed February 9, 1953y for Porous Wall. .Construction and Method of Manufacture. Included inthe objectsof myinvention arez.

First,-.toy provide a methodof constructing al porous wall..wherein the wall may be made tubularin form or tapered-orfarranged to forma venturi-throat or nozzle orvwhich. maybey reformed from. such initial ,shapes into `asymmetrical..rforrn yor. :cut vand reformed .into a sheet.

Secondrlto providefa method of constructing a lporous wall..wherein..the pore spacesmay be accuratelycontrolled so that not. only is .the =wall of. uniformporosity,y but the ,sizedir.ection',. and tortuousness. of..-the poreV spaces may be accurately predetermined .so.asto meet specic needs;

.thatis, .theporesmaybe normal .to thewalllsurface, in-

c1ined,.varying `in area, or. ,cfa labyrinthnature.

Third, .to provide a method of. constructing `a porous wall whereby.l thewall mayhave a controlled variation -in porosity to .predetermine relative flow of -fluids within different areas.

Fourth,l to provide a method of constructing `a porous l through 's4-3 vor Figure 1.

` v Figure 4 is an. exaggerated, fragmentary, 'sectional'view 'showingsuccessive layers of a porous wall constructed iny .accordance with my method.

Figure 5 is a transverse, sectional view thereof through 5-5 of Figure 4.

Figure 6 is an exaggerated, sectional view similar to Figure. 2 by showing a modied form of my porous wall constructed in accordance with 'my vmethod in which the porosity variesk between the two surfaces of the wall -construction.

Figure 7 isa udiagrammatical View showing my porous wall-in the process-of construction in which two layers of wire comprising my formingdayers of vthe porous wallare shown in juXtapositionbefore heating.'y

Figure 8 shows these wiresasthey bond togeth'erin the course' of heating. Figure V9 \is a fragmentary, sectional view similar to Figure 7 showing the wires coated or plated.

Figure 10 is a similar view-showing the coatedwires 'af-ter; heating wherein the coating of adjacentwires'is lfused together.

Figure .'11 is a fragmentary, sectional view indicating y diagrammatically: an arrangement'ofvpore-spaces tending tinducetanlgential yflow fof Yfluid. 1

Figure'tlZ is la .'diagrammatical, isecti-onall viewrofta porous wall constructed in accordancewith 'my method as it appears when flat andar-ranged .with the-porevspaces sloping `relative'.Y tolthe `surfaces fof thewallconstruction.

Figure' 13: is a perspective viewtoff a porous -wallfcylinder: constructed in :accordance withf'fmy method.

Figure ...14 isra-diagrammatica1.viewvof a cone constructed :in accordance `with 'myy method;v i"

Figure. :a .isalsimilardiagrammaticalv view showing a :venturif'nozzle and .rocketsmotor combustiony chamber constructed in='accordance^with myrmethod. i

Figurewl 'illustrates diagrammatically.y in cross-section a turbine blade constructed in accordanceu withl my lIlehOdL'; i

Figure: S17 `isia .diagrammatica'lt sectional :view' showing a .modified formfof. turbine; blade utilizing*the tangential porezarzrangementrepresented imzFigures 1L andi.fl2.

Insthe; exerciseaof .my inventiomzfl .windnonez orf more 4iinefwireson tota mandrel'havingtheshape'of thedinished objectl or a shapeifrom whichnthenished .ohjectzcan be developed-.f Essentiallysuch a mandrel .is 'a gurer'of .reivolution suchxas a cylinder, icone-:or ymore complezcshape suc-h. as a ventur-iithroat oran Iapproximation of; a Ifigure of revolution-:such .as vanellipserorra polygon'or'an'asymmetrical.gure. offpositive cunvaturet .By controlling` the mannerin 'whichethe wire is vwoundwon-:the mandrelV and by/controllingthe:crossfsectionf of .the wire itself; a porous wall mayV beconstructed, .theft porosity ofrwhich may Vbe both. uniform, or, if z desired;4 nonuniform, or; graduated, butV in any case 'the'V pore. Aarrangement .is t predictable.; 'to a close degree... f

Therwire iswound-fona mandrel capable of withstanding ,thebondingstemperature -of xthe.=material comprising the. wire. Thus .themandreLmay be formed of ceramic materialor. `formed .of metal--andx.coated fwitha .ceramic material. l, After...the` wirei hasbeenwoundifto` form-..-a plurality of laminations, thelmandrel, withithe wire thereon,. is .subjected` to heatingftemperatures. Acausing the. .contacting surfaces of .the laminations of wire yto f bond together.

While1thef-wire may have a wide-variety of. cross-sectional confgurations such as circular, rectangular, or ellipsoidal cross-section; ithas been found .that a relatively r 4flatwire isadvantageous... Forrexample, a .wireattened lto a thickness-to-width.ratio` of two-to-one. Thismay be accomplished by running the wire between :rollers either prior to winding or in the course of winding therwire on the mandrel. The at configuration provides. a :maxi- Amumiarea over. whichthe successive laminations of .wire are in pressure contact and -thus insuresan. adequate-area bonded by heating.

' The cross-section or. .area of the wire varies. withthe intended use andthesize of. themandrel on `which 1it:is wound. The larger themandrelxthemore.,coarseythe wire 'which maybe used. However,.in..any. case extremely line. Wire .may be used. For. texamplefwire two .thousandths in diameter., flattened to onethousandth inthickness has been used with success.

z Itlhas been found feasible r'sttovprefbond. the wire While on the mandrel,A then remove the mandrelfsubject the porous wall formed by the wire to mechanicalr pres.- sure, and then rebond. Also,- the Iwiremay be wound in cylindrical 'form Vas shown in Figure l3` and .then .slit lengthwise,.flattened into a sheet, and passed between rollers, Vthis being done after a preliminary bonding...

Aslmentioned .hereinbefo're, the. wiremay be `wound jon itself to produce `a wide'variety of porous conditions. Perhapsthe simplest \form"invol'ves"winding -th'e wire at 'a uniform rate back `and forth.over a .rotating cylinder. By controlling they relative rateY of rotation` Vand feed,'; the succeeding laminations of the wiremay be stacked 4in such ay wayI that vertical-pores may be formed. Thus, a's"sh0wu in Figures 1, 2, and 3, the wire strands 1 may be wound to form channels 2 parallel to each other and to the surfaces of the wall thus formed. If the wires are laid uniformly, they may define ports 3 which extend normal to the two surfaces of the resulting cylinder or other figure of revolution. The porosity is controlled by the closeness with which the wires are wound.

The manner in which the wire may be fed on to the rotating mandrel may be so regulated that succeeding layers do not place the ports in alignment. Thus, as shown in Figure 4, if the succeeding layers are staggered, the ports 3 are not connected except through the channels 2. The result is that a multiplicity of labyrinth passages are formed, which, however, may be uniformly spaced and quite predictable in character. This type of construction is particularly suitable for porous walls to be used as filters.

It is sometimes desirable that the porosity of the resulting structure vary from one side to the other. This may be accomplished by altering the cross-sectional configuration of the wire as succeeding laminations are wound on the mandrel. This may be done as the wire is wound by gradually or intermittently changing the adjustment of the flattening rollers through which the wire passes. Thus, the first laminations of the wire may be fiat, as indicated by 4 in Figure 6, and succeeding layers rendered less at until the inal layer may be square or round as indicated by 5 in Figure 6.

It is, of course, not necessary, in order to have relatively straight pore spaces, that these pore spaces be normal to the surfaces of the finished wall. By proper control of the rate of the feed, the succeeding laminations of wire may be displaced slightly so that the resulting pore space is essentially tangential as indicated by 6 in Figures l1 and 12. In this regard, it will be observed that in forming a cylinder the axes of the pore spaces my be tangential as well as provided with a slope directed toward one end or the other of the cylinder.

As indicated hereinbefore, the mandrel on which the porous wall is formed may take the shape of the finished object, providing such object is a figure of revolution, or an approximation thereof such as an ellipse or polygonal.

Figure 13 illustrates a cylindrical form 7; Figure 14 a conical form 3; and Figure l5 a more elaborate form which represents a nozzle 9 and a chamber 10 of a rocket motor. In this regard, by varying the rate of progress of the wire as it is being wrapped, the resulting porosity may be varied so that, for example, in the construction of a rocket motor, greater porosity may be provided at the regions in which greater introduction of uid is desired.

lt is possible to cut a porous wall cylinder after bonding so as to form a flat sheet. Such sheet may then be reformed. For example, in Figure 13, the cylinder may be cut along the line 11 and formed into a at sheet.

The sheet may be cut to form the two sides of a turbine blade 12 and the sides welded together at the leading and trailing edges as indicated by 13 and 14. If this is done, the pore spaces may have the essentially tangential alignment 6 referred to in regard to Figures ll and 12. It is not necessary, however, to cut the cylinder or other generated shape. Instead such member may be pressed into the desired final shape. In this case, a turbine blade 15 is indicated in Figure 16 which is without seams or welds.

The metal comprising the wire is determined by the use for which the porous wall is intended. Thus, steel, copper, titanium, molybdenum wires, as well as alloys, to mention only a few, may be employed to meet specific conditions. Still further as shown in Figures 9 and 10, the wire may be plated or otherwise coated as indicated by 16.

In this case, the bonding temperature need only be high enough to fuse the coating material. For example, a copper-plated Asteel Wire would thus be capable of 4 being bonded or fused at a lower temperature than unplated steel wire.

It should be observed that the wire is wound under tension so that a firm physical contact is maintained between succeeding laminations of the wire. It is this contact pressure which insures adequate bonding between the laminations in the course of heating.

As pointed out above, the wire is wound under high tension and, as a result, high radial pressure is exerted between the wires at the point of crossing and that tension exists in the completely wound structure while it is still on the mandrel. The initial bonding is accomplished by heating the wound wire while still on the mandrel and the pressure exerted by wire tension provides the required pressure for effecting a secure bond at the temperatures employed. After the structure is removed from the mandrel and compressed to a liner dimension, the portions of the wires adjacent the initial bond are deformed and the area of contact between the wires is extended or increased. Since the wire is actually deformed and still tightly wound, pressure exists between the wire surfaces at the extended areas of contact and the final heating results in bonding the wires, by heat and the existing pressure, to provide the required bond. During the compression of the porous wall after removal from the mandrel, the wires of the laminations are forced closer together, thus producing passages of even smaller dimension than existed at the finish of the shaping and permits construction of porous walls with extremely fine passageways therethrough and permits accurate control of the uniformity and porosity of the product.

As has been indicated hereinbefore, the spacing between individual convolutions of wire and the relative position of the wires comprising succeeding convolutions makes possible the construction of a porous wall having precisely the selected porosity and resistance to flow; that is, with a given porosity the resistance to ow may be increased or decreased, depending on the relation between succeeding laminations of the wire.

Whether la single wire or a multiplicity of wires are used, the winding pitch is such that the wires of succeeding layers cross at a substantial angle with the result that the resulting wall structure, for example, the cylinder shown in Figure 13, will have favorable strength longitudinally as well as circumferentially.

lf a single wire is used, it follows that many traverses of the wires are required before the space between succeeding convolutions of the wire may be filled and a lamination completed.

This, of course, results in crossing of the wires at periodic points along the figure of revolution. Any increase in thickness along these points is eliminated after bonding by pressing or running the wall structure between rollers. It, of course, follows that in winding the wire back and forth across the mandrel, the pitch must change to zero and reverse at each end with the result that there is a build-up at the extremities of the figure of revolution. If the resulting decrease in porosity in these end regions is objectionable in the final production, these portions may be trimmed off after sintering. However, in many cases these ends will be welded or otherwise secured to other members, and the lack of porosity and correspondingly increased density and strength is advantageous.

It is necessary, of course, that the ends of the porous wall figure wound on the mandrel remain in place and not shift axially. If the winding pitch angle is less than 20, the frictional contact between the wire and the mandrel is sumcient to prevent axial shifting of the wire.

However, in winding the wire at pitch angles greater than 20 it is necessary to pass the wire as a chord across the end of the mandrel. The location of the chord path is such that the angle formed by the subtended: are has a value equal to twice the pitch angle.

By so winding the ends `of the figure forming the porous pressure iilter may need greater circumferential strength.

While it is not necessary to wind over `the end of the mandrel or over a shoulder thereon if the pitch angle is less than 20, it has been found that the uniformity is improved if this is done, particularly in the winding of large diameter figures.

While the method herein described is intended primarily for the forming of porous wall structures of metal wire, it may be used to wind wire coated with a fusible plastic material, or for that matter wire formed entirely of plastic material, providing the nature of the mandrel permits fusing together or bonding of the wire at the cross points.

Having thus described certain embodiments and applications of my invention, I do not desire to be limited thereto, but intend to claim all novelty inherent in the appended claims.

- I claim:

1. A method of forming porous wall structures characterized by: forming a ligure of revolution by helically winding wire under tension about a mandrel having a surface of material incapable offusing with said wire, to form at least four successive laminations having spaced parallel wires therein, winding said wire successively in opposite directions whereby each wire crosses underlying wires in mutual bearing contact therewith; initially bonding said laminations by heat and pressure while on said mandrel and whilel their wires are in bearing contact with the wires of adjacent laminations to fuse said wires together; removing said figure of revolution from the mandrel; compressing said figure to reduce the thickness thereof, to reduce the size of the spaces between wires, and to extend the area of contact between the wires; and thereafter again heating said laminations to fuse said wires together throughout the extended areas of contact therebetween.

2. A method of forming porous `wall structures as set forth in claim 1 which is further characterized by: directly superirnposing the wires of alternate laminations whereby radially directed pore spaces are defined by a plurality of laminations. f

3. A method of forming porous wall structures as set forth in claim 1 which is further characterized by: offsetting the wires of successive laminations having the same direction of pitch whereby the pore spaces formed between a plurality of laminations define axes disposed in acute angular relation to the surfaces of said laminations.

4. A method of forming porous wall structures as set forth in claim 1 which is further characterized by:

staggering the location of the wire comprising a plurality of laminations thereby to produce labryinth pore spaces through said laminations.

5. A method as dened in claim 1 including the step of slitting said gure of revolution longitudinally and flattening the same after removal from said mandrel and wherein said step of compressing said laminations is performed by passing said attened figure between rollers.

6. A method of forming porous turbine blades characterized by: forming a gure of revolution by winding wire under tension about a ceramic coated mandrel to form successive laminations, the wires of successive laminations being wound in traversing directions whereby the wires thereof cross and are in mutual bearing contact;

initially bonding said laminations by heat and pressure while on said mandrel and with their wires in bearing Contact with the wires of adjacent laminations to fuse said wires together; removing said figure of revolution from said mandrel; compressing said figure to reduce the thickness thereof, to reduce the sizeof the spaces between wires, and to increase the area of bearing contact between the crossed wires of successive laminations; and again heating said laminations to fuse said wires together at the increased area of bearing; and deforming said figure of revolution into'the profile of a turbine blade.

7. A method of forming porous hollow asymmetrical body characterized by: forming a figure of revolution by winding wire under tension about a mandrel to form successive laminations, the wires of successive laminations being wound in traversing directions whereby the wires thereof cross and are in mutual bearing contact; initially bonding said laminations by heat and pressure while on said mandrel and with their wires in bearing contact with adjacent laminations to fuse said wires together; removing said figure of revolution from said mandrel; compressing said laminations to reduce the thickness of said figure and the size of the spaces between wires while also increasing the area of bearing contact between the crossed wires of successive laminations; and again heating said laminations to fuse said wires at said increased areas of contact; and deforming said figure of revolution into the profile of an asymmetrical body.

8. A method of forming a porous wall structure characterized by: helically wrapping wire under tension on a ceramic-coated mandrel to form successive laminations of wire, at a pitch angle not greater than twenty degrees, the pitch angle of successive laminations being in opposite direction wherein the wires cross at a multiplicity of points; initially bonding said laminations by heat and pressure while said figure is intact on said mandrel to effect at least a partial fusion of said wires at their points of contact; removing said bonded figure from said mandrel; compressing said ligure to reduce the thickness thereof, to reduce the size of the spaces between wires, and to extend the area of contact between wires; and thereafter again heating said laminations to fuse said wires together throughout the extended areas of contact therebetween.

References Cited n the le of this patent i UNITED STATES PATENTS 1,198,349 Heany Sept. 12, 1916 1,644,728 Jahnke Oct. 11, 1927 1,714,989 Schlaich May 28, 1928 2,100,159 Curstadt Nov. 23, 1937 2,351,152 Schick June 13, 1944 

